The output signals of broadband lambda probes are analyzed by external circuit elements, which additionally serve the purpose of adjusting and monitoring the operating parameters of the broadband lambda probe and of monitoring the cable connections. In the process, polarization voltages that must be taken into account when adjusting the pump voltage and when analyzing the output signals occur both at the Nernst cell and the pump cell of the broadband lambda probe. Although it is possible to specify theoretical values for the polarization voltages for the various types of broadband lambda probes, the actual values deviate from these values, sometimes considerably, because of manufacturing variances and aging effects at the probe.
An improved electrical circuitry is discussed in the applicant's patent document DE 10 2008 001697 A1; in addition to operating the exhaust-gas sensor, this circuitry makes it possible to record information about the operating state of the broadband lambda probe which is used there as exhaust gas sensor, to store such information and to forward it to a superposed engine control via a digital interface. This system allows a diagnosis of the cable connections between the electrical circuit elements and the broadband lambda probe with regard to short circuits and interruptions and the maintaining of the voltages allowable at the terminals. The operational readiness of the exhaust-gas probe is detectable and its electrode polarization and aging can be monitored on a continuous basis. To carry out these measurements and to adjust the various operating states, the electrical interconnections of the broadband lambda probe differ in successive switching states of the control electronics, and the broadband lambda probe is therefore switched in different manners electrically. In the process, previous switching stays may have an effect on the measurements. For example, a switching state may lead to an undesired polarization of a Nernst cell of the broadband lambda probe, which results in a falsification of the measured value of the Nernst voltage at the Nernst cell in a subsequent switching state.
The document DE102010000663 A1 of the applicant describes a device for operating a broadband lambda probe in the exhaust tract of an internal combustion engine and for acquiring information about the operating state of the broadband lambda probe. The device makes it possible to diagnose cable connections between the electronics in order to control and analyze the signals of the broadband lambda probe with regard to interruptions and short circuits. In addition, the device makes it possible to adapt a charge exchange correction, as it may be required due of capacitances between supply lines and due to measures aimed at suppressing interference.
In the related art, the polarization of a broadband lambda probe during an active operation is able to be determined only to a highly restricted degree. However, because of aging effects at the exhaust-gas sensors, such a determination would be advantageous for improving the measuring precision at different operating points of the internal combustion engine.